In a mobile communications system, due to requirements of network coverage or network optimization, a beam direction of a base station antenna on a pitch plane needs to be adjusted. For example, a beam on the pitch plane may be adjusted by using an adjustable phase shifter. A working principle of the adjustable phase shifter is to adjust a downtilt of the beam of the antenna by changing phase distribution of each antenna element in the array antenna. In this way, not only a main beam direction can be continuously adjusted, but also it can be ensured that a beam on a horizontal plane is not deformed. There are mainly two types of adjustable phase shifters: a dielectric phase shifter and a physical phase shifter. The dielectric phase shifter implements a phase shift by changing a waveguide wavelength, and the physical phase shifter implements a phase shift by changing a length of a transmission path of an electromagnetic wave. However, as a quantity of remote electrical tilt antennas increases, a filter needs to be added at a front end of a phase shifter, to ensure that frequency bands do not interfere with each other, thereby increasing inter-frequency isolation. Currently, most remote electrical tilt antennas use a separate filter and a separate phase shifter, to implement an inter-frequency isolation function and a downtilt adjustment function. A separate filter and a separate phase shifter increase costs of a remote electrical tilt antenna and difficulty of design, which results in a complex connection of an entire main feeder network. As a result, a quantity of screws or welding points is increased, and magnitude and stability of PIM are reduced.